Engine cooling fan spacer structure

ABSTRACT

A spacer for mounting an engine cooling fan to a drive structure in spaced relation thereto, with the spacer having a forward centering portion engageable with the fan in centering relation, and having a rear pilot recess for receiving a pilot shaft of the drive structure, and with the pilot recess having a peripheral wall defining a series of circularly spaced elongated ribs of uniform internal diameter for engaging the pilot shaft. Circularly between these ribs, the wall of the pilot recess has surface areas which progressively taper as they advance more deeply into the recess.

United States Patent [191 Hecht i [451 July 23,1974

[ ENGINE COOLING FAN SPACER STRUCTURE Inventor: Jay R. Hecht, 17847Cathedral Pl.,

. Encino, Calif. 91365 1 Filed: Nov. 9, 1972 Appl. No.: 304,917

U.S. Cl 64/6, 64/5, 64/4,

Int. Cl Fl6d 3/00 Field of Search 64/6, 8, 5, 4, 3, 1 C, 64/1 R, 9;123/4146, 41.11, 41.12, 41.65; 417/201; 287/53 SS, 56; 308/29 ReferencesCited UNITED STATES PATENTS 6/1967 Amend et al. 64/9 R 3/1970 Dillard123/41.11

as i

3,702,200 11/1972 Carman 64/9 R Primary Examiner-Samuel Scott AssistantExaminer-Randall Heald Attorney, Agent, or Firm-William P. Green [5 7]ABSTRACT 14 Claims, 5 Drawing Figures 1 I ENGINE COOLING FAN SPACERSTRUCTURE BACKGROUND OF THE INVENTION engines, the fan for circulatingair through the radiator is driven by a shaft which is located behindthe radiator, and which usually serves also as the water pump shaft.This shaft itself may in turn be driven by a belt, engaging a sheave orpulley disposed about the shaft.

In order to locate the fan in close enough proximity to the radiator toproduce an optimum flow of cooling air through the radiator, the fan maybe mounted to its drive structure by means of a spacer which projectsthe fan forwardly a predetermined distance from its driving shaft.Thisspacer may be centered with respect to the driving shaft byreception of a forward portion of that shaft within a pilot recessformed in the rear of the spacer. Heretofore, it has been feltnecessary, in forming this pilot recess, to first cast the spacer with aslightly tapered recess at the proper location, and then machine thewall of the recess to a slightly increased diameter cylindricalconfiguration adapted to fit closely on the mating pilot shaft orprojection and assure rotation of the driven fan about exactly the rightaxis. This two step process has unduly increased the cost of the partand introduced a possibility of slight misalignment as between themachined wall of this recess and other portions of the spacer.

SUMMARY OF THE INVENTION I The present invention provides a uniquespacer which is specially designed to eliminate the above discussedmachining operation', and to enable the spacer to be completely formedin a single casting or molding operation. The production cost of thespacer is in this way substantiallyreduced, and the concentricity of thepilot recess with respect to the remainder of the spacer is morereliably assured than where the rear recess is completed by a separatemachining operation after initial casting. i

To attain these results, the wall of the pilot recess is shaped to forma series of circularly spaced elongated ribs, which project radiallyinwardly beyond a number of circularly intermediate portions of therecess wall between the ribs. Along their inner sides, these ribs haveinnermost surfaces which extend at a uniform or unchanging radialdistance from the axis of the spacer as they advance progressively moredeeply into the recess, and which therefore can locally engage andclosely fit an externally cylindrical surface of the mating pilot shaft.Stated differently, these innermost surfaces of the ribs do not advanceeither radially inwardly or radially outwardly with respect to the axisas they advance along thelength of the ribs. The intermediate surfaceareas circularly between the ribs, on the other hand, are shaped togradually taper toward a reduced diameter as they advance more deeplyinto the recess. Desirably, these intermediate tapering surface areashave circular extents much greater than the ribs, and

act by their presence to supply enough draft to the overall recess toallow the recess to be cast in a single operation in spite of the factthat the ribs themselves do not taper. Further, these ribs can in mostinstances have a tighter and closer fit on the coacting shaft than ispossible in the case of a circularly continuous precisely cylindricalrecess or bore, since the ribs engage the coacting shaft at onlyrelatively small localized areas, and can if necessary be deformedslightly by the shaft, upon assembly of the parts, to facilitate suchassembly even with a very close fit of the parts.

BRIEF DESCRIPTION OF THE DRAWING The above and other features andobjects of the invention will be better understood from the followingdetailed description of the typical embodiments illustrated in theaccompanying drawing, in which:

FIG. 1 is primarily an axial sectional view through an engine fanmounting assembly embodying the invention;

FIG. 2 is an enlarged transverse section taken on line 22 of FIG. 1;

FIG. 3 is an axial section taken on line 3-3 of FIG.

FIG. 4 is a further enlarged view corresponding to a portion of FIG. 2;and

FIG. 5 is a reduced scale representation of a variational arrangementutilizing two spacers together.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, I have representedat a conventional intemal combustion engine cooling fan, which ispositioned behind a radiator 11 to draw a flow of air through theradiator in a rightward direction as viewed in FIG.- 1. The engine iscooled by water which circulates through radiator 11, and which ispumped through the engine block, radiator, and the remainder of thecooling system by a conventional water pump represented at 12. This pumpincludes the usual impeller 13 mounted on an externally cylindricalshaft 14 which is journaled by bearings 15 to turn about an axis 16relative to the housing 17 of the pump. The bearings may be receivedwithin shallow grooves in the outer cylindrical surface of shaft 14, toserve as both centering and thrust bearings. As will be understood, thehousing or stator 17 of the water pump is mounted stationarily on theblock of the engine.

Forwardly of the pump 12, shaft 14 carries a structure 18 which isdriven by the engine through an endless fan belt 19. This structure mayinclude a rigid tubular element 20 which is rigidly secured to and turnsshaft 14, and which has an annular radially outwardly projecting flange21 disposed directly transversely of axis 16. To the forward face offlange 21, there is mounted a radially extending portion of a part 22,whose periphery forms an annular groove 23 within which the belt 19 isreceived in driving relation. Element 22 may be secured to part 20 inany appropriate manner, as by welding at 24, or otherwise. The forwardface 25 of part 22 is planar and perpendicular to axis 16 of the shaft.

The fan 10 may havea flat mounting portion 26 perpendicular to axis 16and peripherally carrying a series of circularly spaced vanes 27 adaptedto produce an axial flow of air upon rotation of the fan. At its center,the portion 26 of the fan contains a circular opening 28, which isutilized for centering the fan with respect to rotary axis 16. At aseries of evenly circularly spaced locations (typically four suchlocations), the fan contains apertures 29 through which axial bolts 30extend. The bolts are utilized to secure the fan to drive struc- 3 ture18, with a spacer 33 embodying the invention tightly clamped between thefan and the drive structure. As seen best in FIG. 2, the spacer has atthe location of each of the bolts 30 a radially outwardly projectingportion 34, containing an axially elongated and also radially extendingand radially outwardly opening slot 35 within which the associated bolt30 is received. The width w of each of these slots or grooves 35 isdesirably substantially the same as the diameter of the shank of theassociated bolt 30, so that the bolt is a fairly close fit within thegroove, and assists in maintaining the spacer and other parts againstrelative rotation.

At its rear end, each of the bolts 30 extends through an opening 36 inpart 22 and has an externally threaded portion 31 which is connected tointernal threads 32 formed in an associated one of several circularlyspaced openings in flange 21. The forward ends of the bolts haveenlarged heads 37 which bear against the portion 26 of the fan to clampit tightly rearwardly against the spacer. I

The spacer is desirably rigid, and may be cast of an appropriate metalhaving sufficient strength and stiffness to serve the intended function.At its forward end, the spacer has a front planar surface 38 disposeddirectly perpendicular to axis 16 and against which the rearcorrespondingly planar and transverse surface 39 of portion 26 of thefan abuts tightly. At its center, the forward face of the spacer forms aforwardly projecting pilot lug 40, having an axial extent correspondingapproximately to the thickness of portion 26 of the fan, and projectinginto the central opening 28 of the fan. The outer surface 41 ofcentering lug 40 is desirably cylindrical about axis 16, and of adiameter corresponding to the diameter of the internal surface formed bythe fan within opening 28, to engage that surface essentially annularlyabout axis 16, and assure concentric mounting of the fan with respect tothe spacer.

The back surface 42 of the spacer is also planar, and perpendicular toaxis 16, and abuts against the forward planar transverse surface 25 ofpart 22. At the center of this rear surface'42, the spacer contains apilot recess or hole 43, into which the forward end of shaft 14projects. As seen best in FIGS. 2 and 4, this recess is definedperipherally by a generally annular wall 44, which is shaped to define aseries of circularly spaced radially inwardly projecting ribs 45 forengaging the outer cylindrical surface 46 of shaft 14 in a precisecentering or piloting relation. For best results, there should be atleast three such ribs spaced equal circular distances apart (spaced 120degrees apart in the illustrated threerib arrangement). Preferably, theribs extend directly axially with respect to main rotary axis 16. Also,the ribs may have the illustrated convexly rounded crosssectionalconfiguration, to each engage the outer surfaceof the shaft through onlya very small portion of the circular extent of the recess wall, and morespecifically in essentially line contact axially of the spacer. In orderto effectively engage the external cylindrical surface of the shaft, theinnermost surfaces of the ribs at 47 extendat a uniform or unchangingradial distance r from the axis 16 as they advance axially inwardly intothe recess, and desirably through the entire axial extent ameter as theyadvance axially inwardly into the recess. More specifically, as seen inFIG. 3, these intermediate surface areas 49 taper progressively but verygradually in radius from the location 50 at the entrance end of recess43 to the axially inner end wall 52 of the recess,

at which location the areas 49 desirably reach a minimum radiusapproximately equal to radius r of the innermost surfaces of the ribs.Thus, the three intermediate surface areas 49 may be considered asforming together a frustoconical composite surface interrupted only bythe three ribs 45. It should also be noted that the circular extents ofthe individual intermediate surface areas 49 should desirably beconsiderably greater than (preferably several times as great as) thecircular extents of the individual ribs. As will be apparent, the taperof the surfaces 49 gives the recess as a whole sufficient draft toenable a casting core to be withdrawn axially therefrom, while thenontapering configuration of the narrow ribs provides a sufficientcentering effect to assure precise alignment of the spacer with shaft 14and its axis.

In assembling the apparatus of FIG. I, the spacer 33 may be easilyslipped onto the projecting end of shaft 14 and to a position ofengagement with surface 25 of the drive structure 18, following whichfan 26 may be positioned in front of the spacer, with pilot lugprojecting into center opening 28 of the fan in aligning relation, sothat bolts 30 may then be inserted into posi tion and tightened into thethreaded bores 32 in flange 21 to clamp the parts together in accuratelyaligned relation. v t

In various different engine and radiator installations, spacers of thedescribed type but of different thicknesses may be utilized, in order toassure proper proximate positioning of the fan with respect to theradiator in each engine. Also, in some cases it may be desirable toemploy two or more spacers in additive relation to attain a particularspacing distance for which a single spacer is not available. Such anarrangement is shown in FIG. 5, in whichall of the parts may beconsidered as identical with those shown in FIG. 1 except that twoseparate spacers 33a and 33b have been inserted between the drivestructure 1811 and fan 10a, in lieu of the single spacer 33 of FIG. 1.Each of these spacers is identical with spacer 33, except as tothickness in the direction of axis 16a. The rear spacer 33a engagesdrive structure 18a and its shaft 14a in the same manner discussed inconnection with spacer 33 of FIG. 1, and similarly the forward spacer33b engages the fan in the same centering relation discussed withrespect to FIG. 1. The two spacers are themselves maintained in accurateaxial alignment with one another by reception of the forward pilot lug40a of spacer 33a (corresponding to lug 40 of FIG. 1) within the rearpilot recess 43a of spacer 33b (corresponding to recess 43 of FIG. 1with the outer cylindrical surface of lug 40a engaging the innermostsurfaces of a series of spaced ribs in recess 430 corresponding to ribsof FIGS. 1 to 4.

While certain specific embodiments of the present invention have beendisclosed as typical, the invention is of course not limited to theseparticular forms, but rather is applicable broadly to all suchvariations as fall within the scope of the appended claims.

I claim:

1. A spacer for use in mounting an engine cooling fan 7 to a drivestructure turning about a predetermined axis,

comprising a spacer body, centering means at a first end of said bodyfor locating said fan in a predetermined centered relation relative tosaid body for rotation therewith about said axis, said body having atits second end a recess for receiving a centering projection turningabout said axis, said recess having a generally axially extendingperipheral wall extending about said axis, said wall forming a pluralityof circularly spaced elongated ribs having radially inner surfaces forengaging the outer surface of said projection in centering relation andextending at a predetermined uniform radial distance from said axis asthe ribs advance more deeply into said recess, said wall of the recesshaving interme- 2. A spacer as recited in claim 1, in which said ribsextend substantially directly axially as they advance into said recess.

3. A spacer as recited in claim 1, in which said intermediate surfaceareas have circular extents substantially greater than the circularextents of said ribs.

4. A spacer as recited in claim 1, in which said body has parallelplanar spacing surfaces at its opposite ends disposed perpendicular tosaid axisfor engagingand spacing apart two coacting surfaces.

5. A spacer as recited in claim l, in which said bod has at said firstend thereof a surface disposed transversely of said axis, said centeringmeans including a pilot lug projecting beyond said transverse surfaceand having an external cylindrical surface centered about said axis.

6. The combination comprising an engine cooling fan turning about apredetermined axis, a drive structure for turning saidfan about saidaxis, spacer means axially between said fan and drive structure forholding the fan in predetermined spaced relation tothe drive structure,and means for securing said fan to said drive structure with said spacermeans therebetween, said spacer means including a spacer body havingcentering means at a first end thereof for locating said fan inpredetermined centered relation with respect to said body, said spacerbody containing a pilot recess extending generally axially into itssecond end, there being a pilot projection associated with said drivestructure and projecting into said recess, said recess havingaperipheral wall extending about said projection and forming a pluralityof circularly spaced elongated ribs having radially innermost surfacesengaging the outer surface. of said projection in centering relation,said innermost surfaces of the ribs extending at a uniform radialdistance from said axis as they advance more deeply into the recesstoward said first end of the body, said wall forming intermediatesurface areas circularly between said ribs which commence at a radialdistance from said axis greater than that of said radially innermostsurfaces of the ribs, and out of contact with said pilot projection, andwhich intermediate surface areas taper progressively to a reduced radialdistance from said axis as they of said body and containing a circularcentral opening, said centering means on the body including a pilot lugprojecting into said opening in the fan in centering relation.

8. The combination as recited in claim 6, in which a said drivestructure includes a water pump having a driven shaft with a forwardportion forming said pilot projection extending into said recess.

9. The combination as recited in claim 6, in which said spacer bodyhasfront and rear parallel surfaces disposed directly transversely of saidaxis and engaging transverse surfaces on said fan and said drivestructure respectively, said centering means being a short externallycylindrical pilot lug projecting into a central opening in said fan incentering relation.

10. A spacer for use in mounting an engine cooling fan to a drivestructure turning about a predetermined axis, comprising a spacer body,centering means at a first end of said body for locating said fan in apredetermined centered relation relative to said body for rotationtherewith about said axis, said body having at its second end a recessfor receiving a centering projection turning about said axis, saidrecess having a generally axially extending peripheral wall extendingabout said axis, said wall forming a plurality of circularly spacedelongated ribs having radially inner surfaces for engaging the outersurface of said projection in centering relation and extending at apredetermined uniform radial distance from said axis as the ribs advancemore deeply into said recess, said wall of therecess having intermediatesurface areas circularly between said ribs which commence at a radialdistance from said axis which is greater than said radial distance ofsaid inner surfaces of said ribs from the axis and which intermediatesurface areas progressively taper to reduced radial distances from theaxis in advancing more deeply into said recess, said ribs being ofconvexly rounded transverse cross section and engaging the outer surfaceof said projection along only a relatively small portion of its circularextent.

11. A spacer for use in mounting an engine cooling fan to a drivestructure turning about a predetermined axis, comprising a spacer body,centering means at a first end of said body for locating said fan in apredetermined centered relation relative to said body for rotationtherewith about said axis, said body having at its second end a recessfor receiving a centering projection turning about said axis, saidrecess having a generally axially extending peripheral wall extendingabout said axis, said wall forming a plurality of circularly spacedelongated ribs having radially inner surfaces for engaging the outersurface of said projection in centering relation and extending at apredetermined uniform radial distance from said axis as the ribs advancemore deeply into said recess, said wall of the recess havingintermediate surface areas circularly between said ribs which commenceat a radial distance from said axis which is greater than said radialdistance of said inner surfaces of said ribs from the axis and whichintermediate surface areas progressively taper to reduced radial distances from the axis in advancing more deeply into said recess, saidbody containing axially extending passages through which a series ofelongated bolts are to pass for securing said fan to said drivestructure in spaced relation.

12. A spacer for use in mounting an engine cooling fan to a drivestructure turning about a predetermined 7 axis, comprising a spacerbody, centering means at a first end of said body for locating said fanin a predetermined centered relation relative to said body for rotationtherewith about said axis, said body having at its second end a recessfor receiving a centering projection turning about said axis, saidrecess having a generally axially extending peripheral wall extendingabout said axis, said wall forming a plurality of circularly spacedelongated ribs having radially inner surfaces for engaging the outersurface of said projection in centering relation and extending at apredetermined uniform radial distance from said axis as the ribs advancemore deeply into said recess, said wall of the recess havingintermediate surface areas circularly between said ribs which commenceat a radial distance from said axis which is greater than said radialdistance of said inner surfaces of said ribs from the axis and whichintermediate surface areas progressively taper-to reduced radialdistances from the axis in advancing more deeply into said recess, saidbody having a first transverse planar surface perpendicular to said axisat said first end of the body for engaging'a coacting structure inspacing relation, said centering'means including a short pilot lug atsaid first end of the body projecting beyond the plane of said lastmentioned surface and having an outer centering cylindrical surfacecentered about said axis, said body having at its second end a surfacedisposed transversely of said axis and extending about said recess, saidribs being of convexly rounded cross-sectional configuration, saidintermediate surface areas having circular extents several times-asgreat as the circular extents of said ribs and tapering frustoconicallyrelative to said axis from a diameter substantially greater than saidinner surfaces of the ribs to a diameter approximately the same as saidinnermost surfaces of the ribs, said body having a plurality of passagesat circularly spaced locations for passing bolts therethrough for securing said fan to said drive structure in spaced relatlon.

13. The combination comprising an engine cooling fan turning about apredetermined axis, a drive structure for turning said fan about saidaxis, spacer means axially between said fan and drive structure forholding the fan in predetermined spaced relation to the drive structure,and means for securing said fan to said drive structure with said spacermeans therebetween, said spacer means including a spacer body havingcentering means at a first end thereof for locating said fan inpredetermined centered relation with respect to said body, said spacerbody containing a pilot recess extending generally axially into'itssecond end, there being a pilot projection associated with said drivestructure and projecting into said recess, said recess having aperipheral wall extending about said projection and forming a pluralityof circularly spaced elongated ribs having radially innermost surfacesengaging the outer surface of said projection in centering relation,said innermost surfaces of the ribs extending at a uniform radialdistance from said axis as they advance more deeply into the recesstoward said first end of the body, said wall forming intermediatesurface areas circularly between said ribs which commence at a radialdistance from said axis greater than that of said radially innermostsurfaces of the ribs, and out of contact with said pilot projection, andwhich intermediate surface areas taper progressively to a reduced radialdistance from said axis as they advance more deeply into the body towardsaid first end thereof, said ribs extending substantially directlyaxially and being of convexly rounded cross sectional configuration,said intermediate surface areas having circular extents several times asgreat as the circular extents of said ribs.

14. The combination as recited in claim 13, in which said drivestructure includes a water pump rotor having a shaft with a forwardexternally cylindrical portion forming said pilot projection andengaging the innerv surfaces of said ribs, and including means disposedabout said shaft and forming a transverse shoulder perpendicular to saidaxis, said spacer body having front and rear planar surfacesperpendicular to said axis and engaging said fan and said shoulderrespectively in spacing relation, said centering means including a shortpilot projection extending into an opening in said fan in centeringrelation and having an external cylindrical surface engaging andlocating the fan, said means securing the fan to said drive structureincluding a series of circularly spaced bolts extending axially atcircularly spaced locations and clamping said fan and shoulder againstopposite ends of said spacer body, said body containing a series ofcircularly spaced passages through which said bolts extend.

1. A spacer for use in mounting an engine cooling fan to a drivestructure turning about a predetermined axis, comprising a spacer body,centering means at a first end of said body for locating said fan in apredetermined centered relation relative to said body for rotationtherewith about said axis, said body having at its second end a recessfor receiving a centering projection turning about said axis, saidrecess having a generally axially extending peripheral wall extendingabout said axis, said wall forming a plurality of circularly spacedelongated ribs having radially inner surfaces for engaging the outersurface of said projection in centering relation and extending at apredetermined uniform radial distance from said axis as the ribs advancemore deeply into said recess, said wall of the recess havingintermediate surface areas circularly between said ribs which commenceat a radial distance from said axis which is greater than said radialdistance of said inner surfaces of said ribs from the axis and whichintermediate surface progressively taper to reduced radial distancesfrom the axis in advancing more deeply into said recess.
 2. A spacEr asrecited in claim 1, in which said ribs extend substantially directlyaxially as they advance into said recess.
 3. A spacer as recited inclaim 1, in which said intermediate surface areas have circular extentssubstantially greater than the circular extents of said ribs.
 4. Aspacer as recited in claim 1, in which said body has parallel planarspacing surfaces at its opposite ends disposed perpendicular to saidaxis for engaging and spacing apart two coacting surfaces.
 5. A spaceras recited in claim 1, in which said body has at said first end thereofa surface disposed transversely of said axis, said centering meansincluding a pilot lug projecting beyond said transverse surface andhaving an external cylindrical surface centered about said axis.
 6. Thecombination comprising an engine cooling fan turning about apredetermined axis, a drive structure for turning said fan about saidaxis, spacer means axially between said fan and drive structure forholding the fan in predetermined spaced relation to the drive structure,and means for securing said fan to said drive structure with said spacermeans therebetween, said spacer means including a spacer body havingcentering means at a first end thereof for locating said fan inpredetermined centered relation with respect to said body, said spacerbody containing a pilot recess extending generally axially into itssecond end, there being a pilot projection associated with said drivestructure and projecting into said recess, said recess having aperipheral wall extending about said projection and forming a pluralityof circularly spaced elongated ribs having radially innermost surfacesengaging the outer surface of said projection in centering relation,said innermost surfaces of the ribs extending at a uniform radialdistance from said axis as they advance more deeply into the recesstoward said first end of the body, said wall forming intermediatesurface areas circularly between said ribs which commence at a radialdistance from said axis greater than that of said radially innermostsurfaces of the ribs, and out of contact with said pilot projection, andwhich intermediate surface areas taper progressively to a reduced radialdistance from said axis as they advance more deeply into the body towardsaid first end thereof.
 7. The combination as recited in claim 6, inwhich said fan has a radially inner portion extending transversely ofsaid axis and abutting against said first end of said body andcontaining a circular central opening, said centering means on the bodyincluding a pilot lug projecting into said opening in the fan incentering relation.
 8. The combination as recited in claim 6, in whichsaid drive structure includes a water pump having a driven shaft with aforward portion forming said pilot projection extending into saidrecess.
 9. The combination as recited in claim 6, in which said spacerbody has front and rear parallel surfaces disposed directly transverselyof said axis and engaging transverse surfaces on said fan and said drivestructure respectively, said centering means being a short externallycylindrical pilot lug projecting into a central opening in said fan incentering relation.
 10. A spacer for use in mounting an engine coolingfan to a drive structure turning about a predetermined axis, comprisinga spacer body, centering means at a first end of said body for locatingsaid fan in a predetermined centered relation relative to said body forrotation therewith about said axis, said body having at its second end arecess for receiving a centering projection turning about said axis,said recess having a generally axially extending peripheral wallextending about said axis, said wall forming a plurality of circularlyspaced elongated ribs having radially inner surfaces for engaging theouter surface of said projection in centering relation and extending ata predetermined uniform radial distance from said axis as the ribsadvance more deeply into said recess, said wall of the recess havingintermediate surface areas circularly between said ribs which commenceat a radial distance from said axis which is greater than said radialdistance of said inner surfaces of said ribs from the axis and whichintermediate surface areas progressively taper to reduced radialdistances from the axis in advancing more deeply into said recess, saidribs being of convexly rounded transverse cross section and engaging theouter surface of said projection along only a relatively small portionof its circular extent.
 11. A spacer for use in mounting an enginecooling fan to a drive structure turning about a predetermined axis,comprising a spacer body, centering means at a first end of said bodyfor locating said fan in a predetermined centered relation relative tosaid body for rotation therewith about said axis, said body having atits second end a recess for receiving a centering projection turningabout said axis, said recess having a generally axially extendingperipheral wall extending about said axis, said wall forming a pluralityof circularly spaced elongated ribs having radially inner surfaces forengaging the outer surface of said projection in centering relation andextending at a predetermined uniform radial distance from said axis asthe ribs advance more deeply into said recess, said wall of the recesshaving intermediate surface areas circularly between said ribs whichcommence at a radial distance from said axis which is greater than saidradial distance of said inner surfaces of said ribs from the axis andwhich intermediate surface areas progressively taper to reduced radialdistances from the axis in advancing more deeply into said recess, saidbody containing axially extending passages through which a series ofelongated bolts are to pass for securing said fan to said drivestructure in spaced relation.
 12. A spacer for use in mounting an enginecooling fan to a drive structure turning about a predetermined axis,comprising a spacer body, centering means at a first end of said bodyfor locating said fan in a predetermined centered relation relative tosaid body for rotation therewith about said axis, said body having atits second end a recess for receiving a centering projection turningabout said axis, said recess having a generally axially extendingperipheral wall extending about said axis, said wall forming a pluralityof circularly spaced elongated ribs having radially inner surfaces forengaging the outer surface of said projection in centering relation andextending at a predetermined uniform radial distance from said axis asthe ribs advance more deeply into said recess, said wall of the recesshaving intermediate surface areas circularly between said ribs whichcommence at a radial distance from said axis which is greater than saidradial distance of said inner surfaces of said ribs from the axis andwhich intermediate surface areas progressively taper to reduced radialdistances from the axis in advancing more deeply into said recess, saidbody having a first transverse planar surface perpendicular to said axisat said first end of the body for engaging a coacting structure inspacing relation, said centering means including a short pilot lug atsaid first end of the body projecting beyond the plane of said lastmentioned surface and having an outer centering cylindrical surfacecentered about said axis, said body having at its second end a surfacedisposed transversely of said axis and extending about said recess, saidribs being of convexly rounded cross-sectional configuration, saidintermediate surface areas having circular extents several times asgreat as the circular extents of said ribs and tapering frustoconicallyrelative to said axis from a diameter substantially greater than saidinner surfaces of the ribs to a diameter approximately the same as saidinnermost surfaces of the ribs, said body having a plurality of passagesat circularly spaced locations for passing bolts therethrough forsecuring said fan to said drive Structure in spaced relation.
 13. Thecombination comprising an engine cooling fan turning about apredetermined axis, a drive structure for turning said fan about saidaxis, spacer means axially between said fan and drive structure forholding the fan in predetermined spaced relation to the drive structure,and means for securing said fan to said drive structure with said spacermeans therebetween, said spacer means including a spacer body havingcentering means at a first end thereof for locating said fan inpredetermined centered relation with respect to said body, said spacerbody containing a pilot recess extending generally axially into itssecond end, there being a pilot projection associated with said drivestructure and projecting into said recess, said recess having aperipheral wall extending about said projection and forming a pluralityof circularly spaced elongated ribs having radially innermost surfacesengaging the outer surface of said projection in centering relation,said innermost surfaces of the ribs extending at a uniform radialdistance from said axis as they advance more deeply into the recesstoward said first end of the body, said wall forming intermediatesurface areas circularly between said ribs which commence at a radialdistance from said axis greater than that of said radially innermostsurfaces of the ribs, and out of contact with said pilot projection, andwhich intermediate surface areas taper progressively to a reduced radialdistance from said axis as they advance more deeply into the body towardsaid first end thereof, said ribs extending substantially directlyaxially and being of convexly rounded cross sectional configuration,said intermediate surface areas having circular extents several times asgreat as the circular extents of said ribs.
 14. The combination asrecited in claim 13, in which said drive structure includes a water pumprotor having a shaft with a forward externally cylindrical portionforming said pilot projection and engaging the inner surfaces of saidribs, and including means disposed about said shaft and forming atransverse shoulder perpendicular to said axis, said spacer body havingfront and rear planar surfaces perpendicular to said axis and engagingsaid fan and said shoulder respectively in spacing relation, saidcentering means including a short pilot projection extending into anopening in said fan in centering relation and having an externalcylindrical surface engaging and locating the fan, said means securingthe fan to said drive structure including a series of circularly spacedbolts extending axially at circularly spaced locations and clamping saidfan and shoulder against opposite ends of said spacer body, said bodycontaining a series of circularly spaced passages through which saidbolts extend.